1. Field of the Invention
The present invention relates to a multi-output power conversion circuit for driving an AC motor by obtaining two or more pieces of output from one DC power source, and charging an auxiliary power source.
2. Description of the Related Art
Generally, the configuration of a circuit of an electric vehicle can be the configuration for driving motors using one power source to drive a main motor for driving a vehicle, a motor for a heat pump of an airconditioner, etc.
That is, a power source for driving a main motor has been used to provide a current for other devices such as other motors.
FIG. 1 shows a conventional multi-output power conversion circuit for driving using one power source an AC motor and other devices than the AC motor.
In FIG. 1, 601 denotes a DC power source, 602 denotes a main inverter, and 603 denotes, for example, a three-phase main AC motor having three phase differences through the main inverter 602. The main inverter 602 is configured by six switching elements Tr1 through Tr6, and is PWM-controlled. An auxiliary power source 607 is connected to the same line as the DC power source 601 through a switching circuit 604, a transformer 605, and a rectifying circuit 606. Other devices can be an AC motor in addition to the auxiliary power source 607.
As described in FIG. 1, a power source for driving an AC motor has been conventionally used for other devices by using a power source for driving the main AC motor 603 in providing electric power for the auxiliary power source 607, etc.
As shown in FIG. 1, since insulation is required in providing electric power for the auxiliary power source 607, the switching circuit 604 is required in addition to the main inverter 602, thereby causing the problem that the entire circuit becomes very large.
Thus, the present invention aims at providing a multi-output power conversion circuit capable of having two or more pieces of output using one power supply unit, and realizing a smaller circuit.
To solve the above mentioned problem, the present invention has the following configuration.
That is, according to an aspect of the present invention, the multi-output power conversion circuit of the present invention has output from one DC power source to a polyphase AC motor and other devices than the polyphase AC motor, connects a transformer to the neutral point of the polyphase AC motor, obtains an AC voltage from the transformer using a zero-phase voltage frequency, and outputs the AC voltage to the other devices.
The above mentioned zero-phase voltage frequency refers to a frequency generated at the neutral point of the above mentioned polyphase AC motor, and is different from the frequency driving the polyphase AC motor. In addition, the level of the zero-phase voltage frequency can be lower or higher than the frequency driving the polyphase AC motor.
It is desired that, in the multi-output power conversion circuit according to the present invention, the polyphase AC motor is a first three-phase AC motor, and the other devices are any of an auxiliary power source, a DC motor, and a second three-phase AC motor.
It is also desired that the multi-output power conversion circuit according to the present invention can change a command value when the above mentioned polyphase AC motor is drive-controlled, and can control an AC voltage generated in the transformer.
Furthermore, according to an aspect of the present invention, the multi-output power conversion circuit according to the present invention has output from one DC power source to a polyphase AC motor and other devices than the polyphase AC motor, connects one terminal of a transformer to the neutral point of the polyphase AC motor, connects the other terminal of the transformer to the portion of half the potential of the DC power source, obtains the AC voltage by the zero-phase voltage frequency generated in the transformer, and outputs the AC voltage to the other devices.
It is possible to apply an AC not containing a DC component to the transformer by connecting the other terminal of the transformer to the neutral point of the DC power source.
It is also preferable that the multi-output power conversion circuit according to the present invention connects the transformer to a capacitor in series, and cuts off a DC component.
According to another aspect of the present invention, the multi-output power conversion circuit according to the present invention has output from one DC power source to a polyphase AC motor and other devices than the polyphase AC motor, connects a capacitor to the neutral point of the polyphase AC motor, obtains an AC voltage by the zero-phase voltage frequency from the capacitor, and outputs the AC voltage to the other devices.
Thus, an AC voltage can be obtained by connecting a capacitor instead of a transformer to the neutral point of the multi-output power conversion circuit.
Furthermore, according to a further aspect of the present invention, the multi-output power conversion circuit according to the present invention has output from one DC power source to a polyphase AC motor and other devices than the polyphase AC motor, connects a transformer to the neutral point of the polyphase AC motor, and inserts a capacitor between the neutral point of the polyphase AC motor and the current phase for driving the polyphase AC motor.
In this process, the capacitance of the capacitor is appropriately set, and the current of the carrier frequency component of the polyphase AC motor is led to the transformer through the capacitor. Considering the characteristic of the capacitor, when the frequency gets higher, the impedance becomes lower. Therefore, although the carrier frequency is set high, the current flowing through the transformer does not become low, thereby successfully realizing a smaller transformer.